A method of monitoring the operation of an internal combustion engine is known from European patent document EP-0 344 349. In that method the spark duration is monitored electrically from the primary side of an ignition coil. Monitoring of an internal combustion engine for recognition of combustion failures can be done by two known methods, for example, the method which depends on recognizing faltering in the torque produced by the engine, disclosed in U.S. Pat. No. 4,691,288, and the determination of combustion failure, either by a lambda probe signal, disclosed in European patent document EP-0 387 254, or else by the monitoring of exhaust gas temperature.
These known methods of combustion failure recognition have the disadvantage, however, that the recognition of individual or statistically distributed failures is difficult. Furthermore, the possibility of recognition of a combustion failure is limited to operation of an engine under very small load. Also, the recognition of faltering torque in particular has the disadvantage that mechanical vibrations of a motor and shaking of the vehicle by the roadway make the recognition of failures by that method most difficult. By a falter or faltering of the torque produced by an engine is meant irregular or uneven delivery of torque.